The uplink performance of WCDMA (Wideband CDMA) relies on the ability of the network to control the transmission power, and consequently, the quality of all connected mobile stations. In WCDMA, a radio network controller (RNC) controls the radio base stations (RBSs) such as NodeBs which service the mobile stations within the network. The RNC carries out radio resource management, including determining a quality target such as SIR (signal to interference ratio) using an OLPC (Outer Loop Power Control) function implemented at the RNC. The SIR target is determined on a relatively slow timescale. The RNC determines an individual SIR target for each mobile station serviced within the network. The task of maintaining a particular SIR target is then left to a more rapidly operating ILPC (Inner Loop Power Control) function performed by each RBS responsible for the corresponding mobile station. For example, an RBS may estimate a received SIR of the dedicated physical control channel allocated to a particular mobile station and compare the SIR estimate to the corresponding SIR target determined by the RNC. The RBS issues transmit power control (TPC) commands to the mobile station, ordering the mobile station to increase or decrease its transmission power depending on whether the SIR estimate is below or above the target SIR. Different mobile stations typically demand different SIR targets depending on the current service, radio conditions, movement, etc.
The target SIR provided by the OLPC function performed at the RNC is occasionally modified based on communication quality. For example, a certain targeted number of re-transmission attempts in a Hybrid ARQ (HARQ) process associated with an enhanced dedicated channel (E-DCH) transport channel can be evaluated by the RNC. If the communication quality is too low, i.e. the number of re-transmission attempts is above the set target, the RNC increases the target SIR. If the communication quality is too high, i.e. the number of re-transmission attempts is below the set target, the RNC decreases the target SIR. The SIR target can be similarly modified based on block error rate information. In either case, changes in an SIR target for a particular mobile station are communicated from the RNC to each RBS serving the affected mobile station. As such, the RNC implements the OLPC function and the RBSs implement the ILPC function.
In WCDMA, soft handover can occur from time-to-time meaning that the transmission power of a mobile station is controlled by two RBSs simultaneously. Soft handover is typically implemented in one of two different ways. With partial soft handover, two or more RBSs control the mobile station power to meet the SIR target specified by the RNC. However, data is only received by the RBS responsible for the serving cell. With full soft handover, two or more RBSs control the mobile station power to meet the SIR target specified by the RNC, and the data is received by at least two RBSs out of the two or more RBSs controlling the mobile station power. When no soft handover is performed, the active set of the mobile station contains only the serving cell which has the sole responsibility for transmit power control and data reception. In each of these scenarios, the design choice in WCDMA is typically to maintain the same SIR target in all controlling RBSs by having the OLPC function placed in the RNC, not the RBSs.
With the OLPC function placed in the RNC, there is limited information available to the RNC for determining the SIR target as compared to the additional information available at the RBSs. Consequently, conventional OLPC algorithms typically monitor the block error rate of the payload. Furthermore, placement of the OLPC function in the RNC introduces delay in the algorithm. The delay can be divided into two parts: the delay of the actual signaling between the RNC and the RBSs, which is not negligible; and the additional delay introduced by using the block error of the payload. In the case of HSUPA (High-Speed Uplink Packet Access), the RNC is not aware of any failed transmissions until the transmission is correctly received and relayed up to the RNC. As such, placing the OLPC function in the RNC introduces delay and restricts the information available for determining a suitable mobile station SIR target.